One of the deal-brokers, a leading trade unionist Peter Bunting, said political interference has helped ensure it was never fully implemented.

"I do believe there is interference in the sense, in our view, the then-Minister of Justice was probably beholden to the likes of the DUP for his position as Minister for Justice and I think that probably resulted in him lacking the resolve to tackle this matter head-on," he told a parliamentary committee in Dublin.

Mr Ford told the Press Association: "I utterly refute any suggestion I was beholden to the DUP.

"I certainly had DUP and Sinn Fein support to be elected minister but I made it absolutely clear I was acting on an Alliance agenda, which they accepted before they voted for me."

Mr Ford said the prisoner deal reached six years ago, backed by both the British and Irish governments, included an agreement to end threats to prison officers but those threats continued on social media almost continuously thereafter.

Two serving prison officers have been murdered since 2010.

Mr Bunting, a key figure in securing decommissioning of INLA weapons, said both himself and another mediator Conal McFeely met with Mr Ford's successor Claire Sugden in May, and were assured a speedy review on the agreement's implementation.

But he said they have heard nothing back since then.

Mr Bunting said strip-searching was being used as a "tool to suppress people" in the Roe House wing of the prison, where republican inmates are housed.

"There is both a sectarian attitude and there is political interference towards these people," he said.

The joint committee on the implementation of the Good Friday Agreement was told readily available technology has done away with the need for invasive body searches.

However, Mr Bunting said the practice was part of everyday life in the jail.

Prisoners are also been isolated for extended periods - with one inmate being locked up 23 hours a day for five years - and denied education, he added.

Treatment of dissident republican prisoners in Maghaberry has long been a source of contention.

Some say they are forced to suffer inhumane and degrading treatment while others say they receive favourable treatment compared to the rest of the prison population.

Mr McFeely added that the "question of political interference had to be answered."

Senator Frank Feighan, who sits on the committee and who visited the prison, said there was "a lot of pettiness" involved in resisting reforms.

"I'm concerned about what you are saying about political interference with the minister for justice," he said.

"If that was happening down here it would be a serious national scandal."